A base station antenna including a repeater used in a mobile communication system may have various shapes and structures. Typically, the base station antenna has a structure in which a plurality of radiating elements are appropriately disposed on at least one reflecting plate standing upright in the longitudinal direction.
Recently, a variety of studies have been conducted in order to satisfy the demand for miniaturization and weight reduction of a base station antenna. Among them, in the case of a dual-band dual-polarized antenna, for example, an antenna having a structure in which a second radiating element in a high frequency band of a next-generation advanced wireless service (AWS) band or a 2 GHz band is stacked on a first radiating element in a low frequency band of 700/800 MHz band is being developed.
The antenna may have the first and second radiating elements having, for example, a stacked structure in which a patch-type or dipole-type second radiating element is installed on a patch-type first radiating element. The first and second radiating elements having the stacked structure may have a structure in which a plurality of radiating elements are arranged on the reflecting plate at intervals to satisfy the arrangement of the radiating elements in the first frequency band.
Further, the antenna has a structure in which the second radiating elements are additionally installed on the reflecting plate to satisfy the arrangement of the radiating elements in the second frequency band between the first and second radiating elements having the stacked structure in which a plurality of radiating elements are installed. By the arrangement, it is possible to obtain an antenna gain while satisfying the miniaturization on the whole.
FIG. 1 is a plan view of the existing dual-band dual polarized mobile communication base station antenna, and FIG. 2 is a cross-sectional view taken along the line A-A′ in FIG. 1. Referring to FIGS. 1 and 2, in the antenna having the structure in which the second radiating element is stacked on the first radiating element, patch-type first radiating elements 11 and 12 of a first frequency band (for example, 700/800 MHz band) are arranged at regular intervals on an upper surface of a reflecting plate 1. Further, the dipole-type second radiating elements 21, 22, 23, and 24 of the second frequency band (for example, the AWS band) are stacked on the first radiating elements 11 and 12 or is directly installed on the upper surface of the reflecting plate 1 between the first radiating elements 11 and 12.
Each of the first radiating elements 11 and 12 is made up of upper patch plates 11-2 and 12-2 and lower patch plates 11-1 and 12-1. The lower patch plates 11-1 and 12-1 are connected to a circuit board 111 on which a feeding conductor pattern attached to a back surface of the reflecting plate 1 is formed, by a feeding cable 112 passing through the reflecting plate 1. Further, the second radiating elements 21 and 22 stacked on the first radiating elements 11 and 12 are connected to a feeding network by a feeding cable 212 passing through the reflecting plate 1 and upper and lower patch plates 11-1 and 12-1 of the installed first radiating elements 11 and 12.
In addition, the base station antenna may include a cylindrical radome (not shown) completely enclosing the reflecting plate 1 on which the radiating elements are installed and various signal processing equipments for processing transmission/reception signals therein and an upper cap and a lower cap (not shown) for fixing upper and lower portions of the reflecting plate 1, respectively and sealing upper and lower openings of the cylindrical radome.
Meanwhile, FIGS. 3A-3B are views showing a feeding structure of the first radiating elements of FIG. 1. FIG. 3A is a plan view and FIG. 3B is a rear view. For convenience of explanation, FIGS. 3A-3B show one lower patch plate 11-1 of the first radiating elements and the circuit board 111 for the feeding conductor pattern is a lower patch plate 11-1 and a circuit board 111, and other components will be omitted. Referring to FIGS. 1 to 3B, the lower patch plate 11-1 of the first radiating element 11 is connected to the circuit board 111 attached to the back surface of the reflecting plate 1 by the feeding cable 112 passing through the reflecting plate 1. That is, the feeding conductor pattern of the first radiating element is formed on the circuit board 111 in a printing manner, and has a structure in which feeding points a to d on the circuit board 111 and feeding points a to d on the lower patch plate 11-1 are connected to each other by the feeding cables 112.
At this time, for example, the feeding conductor pattern is formed on the circuit board 111 so that a transmission signal at the feeding point c located diagonally to the feeding point a has a phase retarded by 180°, compared to the feeding point a. Similarly, the transmission signal at the feeding point d located diagonally to the feeding point b also has a phase retarded by 180°, compared to the feeding point b. Therefore, the dual polarization orthogonal to each other is generated at the feeding points a and c and the feeding points b and d on the lower patch plate 11-1 of the first radiating element.
Meanwhile, the upper patch plate 11-2 of the first radiating element is installed to optimize radiation characteristic and is installed by a support (reference numeral 130 of FIG. 2, or the like) of a plastic material 130, or the like so as to be insulated from the lower patch plate 11-1.
As a technique related to the base station antenna having the above-described structure, there is disclosed in Korean Patent Application No. 10-2009-0110696 (Title: Method for installing radiator elements arranged in different planes and antenna thereof, Inventors: four besides Yeon Chan Moon, Filing date: Nov. 17, 2009) earlier filed by the present applicant.
By the way, as disclosed in the above-mentioned Patent Application No. 10-2009-0110696, the structure in which the dipole-type second radiating element 21 is stacked on the patch-type first radiating element 11 has a relatively complicated and a relatively large number of additional accessories for supporting and fixing the first radiating element 11 and the second radiating element 21 are required. Further, in this case, the circuit board 111 for feeding power to the patch-type first radiating element 11 is installed on the back surface of the reflecting plate 1, and a feeding line (for example, feeding cable) of the second radiating element 21 stacked on the first radiating element 11 needs to be installed in a form in which it passes through the circuit board 111 again, or the like, and as a result a space required to install the feeding line on the back surface of the reflecting plate 1 is relatively large. In addition, the installation space of various signal processing equipments including a phase shifter, or the like that is provided on the back surface of the reflecting plate 1 may be limited. As a result, there has been a problem in that the overall size of the base station antenna becomes large.